TMCThis company is form England.England and Australia used balanced armature
or sound powered units on ships also.Two distint models (looks are the same) AP12501
(Australia), AP12591(England)Both of these models may have been used in
both England and Australia

David Clark Company Inc.Model H5090, For full listing of models Click
HereFor parts list Click
HereElements for above headset run about $85.90
each new (elements only)

Sound Powered Communications
CorporationLeft and center are model SPT-500 SP
on far right model SPT-125 SThey also sell a headset which is made by
David Clark

Inside a Sound Powered ElementDrawings and photos of the "insides"
of elements!!Click Here